Message.java

package ru.denull.mtproto;

import static ru.denull.mtproto.CryptoUtils.*;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;

import tl.TL;
import tl.TLObject;

public class Message {
	public int error = 0;
	
	public long message_id;
	public TLObject payload;
	
	public Message(long message_id, TLObject payload) {
		this.message_id = message_id;
		this.payload = payload;
	}
	
	public Message(int error) {
		this.error = error;
	}
	
	public ByteBuffer encrypt(byte[] auth_key) throws Exception {
    //System.out.println("sending raw " + payload);
		if (error != 0) {
			return ByteBuffer.allocateDirect(4).putInt(-error);
		}
		
		int size = payload.length(true);
    ByteBuffer buffer = ByteBuffer.allocateDirect(size + 20);
    buffer.order(ByteOrder.LITTLE_ENDIAN);
      
    buffer.putLong(0);
    buffer.putLong(message_id);
    buffer.putInt(size);
      
    payload.writeTo(buffer);
    
    buffer.rewind();
    return buffer;
	}
	
	public static Message decrypt(ByteBuffer buffer) throws Exception {
		return decrypt(buffer, null, 0);
	}
	public static Message decrypt(ByteBuffer buffer, byte[] auth_key, long auth_key_id) throws Exception {
		if (buffer == null) {
  		return null;
  	}
  	
  	if (buffer.capacity() == 4) {
	    return new Message(-buffer.getInt());
  	}
    
    long _auth_key_id = buffer.getLong();
    
    if (_auth_key_id == 0) {
      long message_id = buffer.getLong();
      int size = buffer.getInt();
      
    	return new Message(message_id, TL.read(buffer));
    } else
    if (_auth_key_id == auth_key_id) {
      byte[] msg_key = new byte[16];
      buffer.get(msg_key);
      
      byte[] encrypted_data = new byte[buffer.capacity() - 24];
      buffer.get(encrypted_data);
      
      int x = 8;
      byte[] sha1_a = SHA1(concat(msg_key, substr(auth_key, x, 32)));
      byte[] sha1_b = SHA1(concat(substr(auth_key, 32 + x, 16), msg_key, substr(auth_key, 48 + x, 16)));
      byte[] sha1_c = SHA1(concat(substr(auth_key, 64 + x, 32), msg_key));
      byte[] sha1_d = SHA1(concat(msg_key, substr(auth_key, 96 + x, 32)));
      
      byte[] aes_key = concat(substr(sha1_a, 0, 8), substr(sha1_b, 8, 12), substr(sha1_c, 4, 12));
      byte[] aes_iv = concat(substr(sha1_a, 8, 12), substr(sha1_b, 0, 8), substr(sha1_c, 16, 4), substr(sha1_d, 0, 8));
      
      ByteBuffer innerBuffer = ByteBuffer.wrap(AESDecrypt(encrypted_data, 0, encrypted_data.length, aes_key, aes_iv));
      innerBuffer.order(ByteOrder.LITTLE_ENDIAN);
      long server_salt = innerBuffer.getLong();
      long session_id = innerBuffer.getLong();
      long message_id = innerBuffer.getLong();
      int seq_no = innerBuffer.getInt();
      int size = innerBuffer.getInt();
      
      return new EncryptedMessage(message_id, TL.read(innerBuffer), session_id, _auth_key_id, server_salt, seq_no);
    } else {
      throw new Exception("Unknown auth_key received");
    }
	}
	
}